This meeting on pulmonary vascular reactivity will be held at the Lost Valley Ranch conference center in Colorado from 10/10 to 10/12/84. During the last few years numerous advances have been made in our understanding of the physiology of smooth muscle and vascular endothelium. In particular, more is known of the interaction between the endothelium and vascular smooth muscle, the actions of leukotrienes and prostaglandins, the importance of calcium flux involving different loci of calcium sequestration within smooth muscle, and the effects of changes in oxygen tension on cellular energy metabolism. However, this new information has not been integrated into our understanding of the mechanisms controlling pulmonary vascular reactivity and applied to the etiologies of pulmonary hypertension. This conference is designed to bring together 35 of the leading researchers in these areas, whose expertise covers biochemistry, pharmacology, physiology, pathology, cardiology and pulmonary medicine. Each will present a 15 minute paper which will be followed by a 15 minute discussion period. It is anticipated that the format of this meeting, which promotes discussion between workers of very different backgrounds, though with a common interest in vascular reactivity, will lead to a better understanding of the mechanisms determining pulmonary vascular tone. Such an understanding will permit better definition and treatment of the causes of pulmonary hypertension. Recent meetings on the pulmonary circulation have tended to be more narrowly focused on primary pulmonary hypertension or the importance of arachidonic acid metabolites in the pulmonary vasculature. The substance of each lecture will be published in order to achieve a wide dissemination of the information and ideas.